The invention disclosed herein pertains in general to air conditioning systems and in particular to maintaining precise control over the temperature of air that is leaving a system or the temperature of water that is leaving a system if the basic concepts of the invention are utilized in a water or other liquid heating system.
The new refrigerant modulated precision control over the leaving medium temperature will be demonstrated herein as applied in a system that is dedicated to supplying fresh outdoor air directly to one or more rooms in a building or, alternatively, by using the ducts of a conventional air conditioning system. Those who are knowledgeable in designing heating, ventilating and air-conditioning systems will readily perceive that the new method of control will have a variety of applications.
It is known that occupants of some buildings acquire respiratory illnesses and other illnesses that are related to poor air quality. These illnesses can and do occur even in buildings that are equipped with conventional air conditioning systems of acceptable design. In cases where the dew point of the treated air is relatively high, conditions will exist in the air distribution ducts that encourage growth of fungi, molds and bacteria which become entrained in the air stream and are inhaled by the occupants of the building.
Air that is supplied to a room or building by way of conventional air conditioning systems often does not have enough dry or dehumidified outdoor air added for maintaining optimum health conditions. Most conventional air conditioning systems take in some outdoor air and mix it in the return air stream, cool and dehumidify it and/or heat it and discharge it into a distribution duct system. However, as skilled conventional system designers know, there are technical limitations and adverse economical considerations that prevent designing for mixing not much more than 15% to 20% of fresh outside air into the conditioned air stream. The permissible amount of outside air is usually governed by expected temperature and humidity extremes in the climate at which the system is installed. Usually, if a large percentage of outside air must be added to air that is circulated in a conventional air conditioning system, the capacity of the system must be increased. This means that the system will be more expensive because of larger condensers, evaporators, compressors, compressor motors and housings will be required.
Because the importance of adequate outside air to the health of occupants has been recognized, building codes are amended to compel adding specified large quantities of outside air to spaces that are occupied by people wherever possible such as in new construction and refurbished buildings. Thus, it becomes important to assure that the temperature of the air leaving the conditioning unit be held at a precise temperature that is comfortable to occupants of a room onto whom the leaving air stream may impinge directly.
A widely used system that is dedicated to admitting outside air to a room or to mix in the ducts of a conventional air conditioner system is a system that is based on controlling separate dampers to define combined and/or alternate air paths for regulating leaving air temperature. The principles of the heretofore most widely used system will be described in detail later. As will be evident, a major problem with this system is that precise control over the leaving air temperature cannot be achieved because dampers can only make gross changes in air flow patterns within a unit but the method cannot control with adequate precision to prevent the temperature from hunting above and below the thermostat set point. Moreover, the system that has been used most extensively up to the time of the present invention is a system that is unduly costly to make, requires a large space in a building and has less than optimized serviceability.